Traditionally, a soda lime glass plate for a building window has been used as a substrate for a plasma display panel. On a surface of the substrate, an electrode comprising Al, Ni, Ag, ITO, a NESA film, or the like and an insulating paste are printed at a temperature of 500-600.degree. C. to thereby form a circuit. Then, frit sealing is carried out at a temperature of 500-600.degree. C. In this manner, the plasma display panel is manufactured.
Therefore, the substrate glass of the type is generally required to have following characteristics.
1 A strain point is equal to or greater than 570.degree. C. in order to reduce thermal contraction upon heat treatment at a temperature of 500-600.degree. C., in particular, 570.degree. C. or more.
2 No warp occurs because a coefficient of thermal expansion matches those of the insulating paste and sealing frit. In other words, the coefficient of thermal expansion is 75-95.times.10.sup.-7 /.degree. C.
3 A volume resistivity of the glass is as high as 10.sup.10 .OMEGA..multidot.cm or more at 150.degree. C. and an alkali component does not react with a thin-film electrode. This is because, if the alkali component in the glass reacts with the thin-film electrode such as the NESA film, an electric resistance of an electrode material changes.
The soda lime glass for a building window has the coefficient of thermal expansion of about 89.times.10.sup.-7 /.degree. C. and no warp occurs if it is used as the substrate of the plasma display panel. However, because the strain point is as low as about 500.degree. C., there is disadvantage that the thermal contraction is great upon the heat treatment at a temperature of 570-600.degree. C.
In addition, the soda lime glass is relatively low in volume resistivity and poor in chemical durability. During the storage or the use over a long period of time, hazing occurs on a surface. This results in a disadvantage that a display screen of the plasma display unit can not be clearly seen.
Taking the above-mentioned situation into consideration, it is an object of the present invention to provide a substrate glass which exhibits little thermal contraction even if heat treatment is carried out at a temperature of 570.degree. C. or more, which has a coefficient of thermal expansion of 75-95.times.10.sup.-7 /.degree. C., and which is high in volume resistivity and excellent in chemical durability as compared with a soda lime glass.
It is another object of the present invention to provide a plasma display unit using the above-mentioned substrate glass.